This application is based upon claims the benefit of priority from the prior Japanese Patent Applications No. 2000-299601, filed Sep. 29, 2000; No. 2000-299602 filed Sep. 29, 2000; and No. 2000-299603 filed Sep. 29, 2000, the entire contents of all of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic balance for measuring the mass of the substance to be weighed and more specifically, to an electronic balance that is easy to assemble and maintain, and that can be downsized, and in addition to this, an electronic balance with an improved lever that moves from the balancing state during load application, and furthermore, an electronic balance that enables the protection of the spring section of the Roberval""s mechanism by improving the mobile range of the Roberval""s mechanism which composes the electronic balance.
2. Description of the Related Art
Hitherto, for this kind of electronic balance, xe2x80x9cELECTRONIC BALANCExe2x80x9d disclosed in the U.S. Pat. No. 4,799,561 is well known.
FIG. 23 is a front cross-sectional view showing the xe2x80x9cELECTRONIC BALANCExe2x80x9d disclosed in the U.S. Pat. No. 4,799,561 as the first conventional electronic balance 80.
FIG. 24 is a perspective view showing to remove the scale plate 89 from FIG. 23.
That is, as shown in FIGS. 23 and 24, the first electronic balance 80 generally comprises a Roberval""s mechanism 81 in which the mobile section 81b with the scale plate 89 provided moves with respect to the fixed section 81a, a lever 83 that operates in linkage with the transfer of the mobile section 81b, an electromagnetic coil 85 that moves and controls the lever 83 to be in the balancing state, a position detection sensor (not illustrated) for detecting the balancing state of the lever 83, and a control section that energizes and controls the electromagnetic coil 85 to calculate and output the mass of the substance to be weighed.
Now the Roberval""s mechanism 81 has a pair of upper and lower parallel Roberval""s sections 86 formed by hollowing out a metal block such as rectangular aluminum, etc. from the one side to a specified shape as illustrated.
In this Roberval""s section 86, a total of 4 thin-wall spring sections 87 are formed, and when a substance to be weighed is placed on a scale plate 89 of the mobile section 81b, the spring section 87 portion is deformed by receiving this load, and the mobile section 81b moves downwards with the level condition maintained by the mobile section 81b. 
In linkage with the shift of this mobile section 81b, the free end 83a of the lever 83 displaces from the balancing position to upwards.
The control section energizes and controls the electromagnetic coil 85 so that the lever 83 is brought to the balancing state based on the output of the position detection sensor, and calculates and outputs the mass of the substance to be weighed in accordance with the current value, etc. to the electromagnetic coil 85 when the lever 83 is in the balancing state.
Hitherto, for this kind of electronic balance, xe2x80x9celectronic weighing apparatusxe2x80x9d disclosed in the Jpn. Pat. Appln. KOKAI Publication No. 11-51756 is well known.
FIG. 25 is an exploded perspective view of the principle section that shows the xe2x80x9celectronic weighing apparatusxe2x80x9d disclosed in the Jpn. Pat. Appln. KOKAI Publication No. 11-51756 as the conventional second electronic balance 90.
That is, as shown in FIG. 25, the second electronic balance 90 has the Roberval""s mechanism 91 and the lever 92 separately formed.
Now, the lever 92 is installed in the form of linking both side sections of the Roberval""s mechanism 91.
And this lever 92 is held between the Roberval""s mechanism 91 and the base member 95 as shown with an illustrated broken line by a plurality of fulcrum member 93 and a suspension member 94.
The lever 83 in the configuration of the first electronic balance 80 is formed integral with the Roberval""s mechanism 81, whereas in the second electronic balance 90, it is formed separately from the Roberval""s mechanism 91, but both Roberval""s mechanism 81 and Roberval""s mechanism 91 are formed by hollowing a rectangular shape aluminum block, etc. from the one section to a specified profile as described above.
Hitherto, for this kind of electronic balance, the xe2x80x9cDEVICE FOR REDUCING THE FORCE IN A FORCE-MEASURING APPARATUS, IN PARTICULAR IN A SCALExe2x80x9d disclosed in the U.S. Pat. No. 5,340,951 is well known.
FIG. 26 is a perspective view showing the xe2x80x9cDevice for Reducing the Force in a Force-measuring Apparatus, in Particular in a Scalexe2x80x9d disclosed in the U.S. Pat. No. 4,350,951 as a third conventional electronic balance 100.
That is, as shown in FIG. 26, this third electronic balance 100 has the Roberval""s mechanism 101 hollowed and formed from the one side section of a rectangular aluminum block, etc. and at the same time, a lever mounting section 102 is formed.
By mounting a separate lever 103 to this mount section 102, an electronic balance 100 is constructed.
Now, as shown in FIGS. 23 and 24, the lever 83 in the configuration of the first conventional electronic balance 80 is hollowed into a specified shape continuously in the width direction from the one section side of a rectangular aluminum block material, etc.
Consequently, in the first conventional electronic balance 80, in order to provide the specified rigidity to the lever 83, the thickness must be increased, causing a problem of increased weight.
That is, because the width of this lever 83 is the same as that of the Roberval""s mechanism 81, it is unable to reduce the weight while maintaining the rigidity.
In addition, in general, in this kind of lever 83, as the lever length is increased, the load applied to the mobile section 81b of the Roberval""s mechanism 81 can be attenuated, and at the same time, the measurement accuracy as the electronic balance 80 can be improved by increasing the displacement rate of the free end 83a of the lever 83 (hereinafter called the xe2x80x9cdisplacement ratexe2x80x9d).
And yet, since with the lever 83 of the first conventional electronic balance 80 with the above-mentioned configuration causes restrictions that the lever length is shorter than the Roberval""s mechanism 81, there is a limit to the improvement of measuring accuracy.
This kind of Roberval""s mechanism 81 is formed with the measurement range of the mass of the substance to be weighed previously specified.
In particular, the rigidity of the whole Roberval""s mechanism 81 and the spring constant of the spring section 87 are set to fit to the measurement of the mass of the substance to be weighed in the relevant measuring range.
The rigidity of this Roberval""s mechanism 81 and the spring constant of the spring section 87 have influences on the start of measurement of the mass of the substance to be measured, that is, the time from when the substance to be weighed is placed until the vibration of the mobile section 81b ends to enable the measurement (response time).
However, in the first conventional electronic balance 80, etc. as described above, the Roberval""s mechanism 81 is formed by hollowing a rectangular aluminum block, etc. from the one section into a specified shape and has a configuration to have a total of 4 pieces of thin-wall spring section 87.
Consequently, in the first conventional electronic balance 80, etc., there is a problem of damaging the thin-wall spring section 87 if external vibration or impact is applied to the spring section 87 located between the mobile section 81a and the fixed section 81b when the Roberval""s mechanism 81 is being transferred to the subsequent assembly step, etc. after forming the Roberval""s mechanism 81.
This problem occurs not only during transportation but also when an unexpected load is applied to the spring section 87 during the assembly step for mounting the Roberval""s mechanism 81 to the supporter 88a of the base frame 88 or when an impact load due to an unexpected matter falling on the scale plate 89 is applied to the spring section 87 via the mobile section 81b while the balance is used after assembly.
Or, as shown in FIG. 25, since the Roberval""s mechanism 91 and the lever 92 are formed separately in the second conventional electronic balance 90, it has an advantage that the manufacture of each component can be carried out more easily.
And yet, because in this second conventional electronic balance 90, the overall size, particularly, the width W becomes the width of the lever 92 added to the Roberval""s mechanism 91, it has the problem of a big size as a whole.
For example, in the second conventional electronic balance 90, when heavier mass is intended to measure, the width W of the Roberval""s mechanism 91 will be increased, but since the overall width becomes constantly wider by the width of the lever 92 added, the balance is unable to be downsized.
In addition, because the base end section 92b of the lever 92 is held by a plurality of fulcrum member 93 and hanging band 94 in the second conventional electronic balance 90, it has a problem of complicated and troublesome assembly and adjustment of the lever 92.
And as shown in FIG. 26, with respect to the third conventional electronic balance 100, it has an advantage of forming the Roberval""s mechanism 101 separately from the lever 103, but since the lever 103 is installed on both sides of the Roberval""s mechanism 101, the overall size, particularly, the width W becomes large, and the electronic balance has a problem of inability to be downsized.
In all the first to third conventional electronic balances 80, 90, 100, generally aluminum is used for the material of the Roberval""s mechanism and the lever.
When the electromagnetic coil or balancing position detection sensor is installed to the free end section of the lever, if the material of the fixing members of these is aluminum, the metal of the same kind used for Roberval""s mechanism and the lever, they are weak against the bend, and in general, stainless steel screws are used.
And yet, since the linear expansion coefficient differs in dissimilar metals such as aluminum and stainless steel, when strain is generated at the screw fixing section, the mounting position of the electromagnetic coil and the balancing position detection sensor vary, causing problems of generating an error in the balancing control, or failure to carry out stable control, and the weighing accuracy is unable to be improved as an electronic balance.
Or, by equipping a plurality of fulcrums to the lever, it is possible to increase the attenuation amount for the free end side during load application and improve the only weighing accuracy had been increased.
However, if a plurality of fulcrums is equipped to the lever, the fulcrums each are formed by the thin-wall spring section, causing problems of increasing the places to be required the process accuracy of only the fulcrums had been increased and not being unable to manufacture easily.
Even if the Roberval""s mechanism and the lever are simply formed separately, when the number of fulcrums increases, there is a fear in that the spring section may be damaged under the component condition up to assembly unless the lever is carefully handled and the balance is unable to be used.
Accordingly, it is an objective of the present invention to provide an electronic balance which can be easily assembled and maintained and can be downsized.
Another object of the present invention is to provide an electronic balance which can be assembled easily and highly accurately and that enables downsizing and can improve the measurement accuracy.
Still a further object of the present invention is to provide an electronic balance that can protect the spring section of the Roberval""s mechanism by improving the mobile range of the Roberval""s mechanism.
In order to achieve the above objectives, according to the present invention,
(1) it is possible to provide an electronic balance comprising:
a Roberval""s mechanism containing a fixed section, a mobile section that is applied with the load of the substance to be weighed and moves in the vertical direction with respect to the fixed section, and a pair of upper and lower Roberval""s sections that link the fixed section and the mobile section,
a lever that has one end, the other end, and fulcrums, is located between a pair of the upper and the lower Roberval""s sections of the Roberval""s mechanism, receives the motion of the mobile section of the Roberval""s mechanism with the one end, and allows the other end to displace via the fulcrums,
balance driving means that is equipped to the other end of the lever and controls the lever to achieve the balancing state,
characterized in that the Roberval""s mechanism and the lever are configured separately,
to the Roberval""s mechanism, a lever housing section is formed for inserting the lever in the longitudinal direction and enabling the lever to be located between a pair of the upper and the lower Roberval""s sections,
to the other end of the lever, a section extending outwards beyond the lever housing section is equipped, and
balance driving means is mounted to the section equipped to the other end of the lever and extending outwards.
In order to achieve the above objects, according to the present invention,
(2) an electronic balance recited in Item (1) characterized in that
the lever is housed in the lever housing section, the mobile section on the one end side is linked and fixed to the mobile section of the Roberval""s mechanism, and the other end side displaces by the specified volume from the balancing state by operating together with the motion of the mobile section of the Roberval""s mechanism.
In order to achieve the above objects, according to the present invention,
(3) an electronic balance recited in Item (1) characterized in that
in the lever housing section, a stepped section which comes in contact with the one side section of the lever along the longitudinal direction of the Roberval""s mechanism and which guides the lever housing position to the lever housing section is formed.
According to the above configuration, inside the Roberval""s mechanism 2, the lever housing section 2b is opened and formed from the one end section 2a side.
The lever 4 is housed and fixed to this lever housing section 2b and the free end 4b is extended outwards in the width smaller than the opening diameter and formed.
By this, balance driving means 6 can be installed to the position outside the Roberval""s mechanism 2, rendering itself capable for easy assembly and maintenance and inspection.
To the lever housing section 2b, a stepped section 22d in contact with the one side section of the lever 4 is formed along the length direction of the Roberval""s mechanism 2 and guides the lever 4 when it is housed, eliminating fixing errors and enabling easy assembly.
In order to achieve the above objects, according to the present invention,
(4) it is possible to provide the electronic balance recited in Item (1) further comprising:
a thin-wall spring section that is equipped to the lever, includes the fulcrums that can obtain the attenuation rate of the specified force from the one end section to the free end, forms the fixed section and the mobile section on the lever, and links these, and
bridges installed between the fixed section and the mobile section of the lever, fixes and supports the position of the fixed section and the mobile section, and is cut off after the lever is fixed to the Roberval""s mechanism.
In order to achieve the above objects, according to the present invention,
(5) it is possible to provide the electronic balance recited in Item (4) characterized in that cutting holes for cutting the bridge are opened at the bridge arranging position of the lever in the Roberval""s mechanism.
In order to achieve the above objects, according to the present invention,
(6) it is possible to provide the electronic balance recited in Item (1) further comprising:
position detection means for detecting the displacement rate of the lever,
a fixed surface formed at the free end of the lever and to which balance driving means is fixed,
a stepped surface formed at the free end of the lever and formed in the direction in which the lever displaces with respect to the fixed surface and formed low with a specified level difference, and
a fixing member of the dissimilar metal different from the lever material for fixing balance driving means and position detection means with respect to the lever,
wherein balance driving means only is fixed to the fixed surface and position detection means is arranged and fixed to the stepped surface.
In order to achieve the above objects, according to the present invention,
(7) it is possible to provide the electronic balance recited in Item (6) characterized in that a restricting member that composes restricting means for restricting the travel amount of the free end of the lever is arranged and fixed.
In order to achieve the above objects, according to the present invention,
(8) it is possible to provide the electronic balance recited in Item (1) characterized in that to the lever, the first reinforcement piece with a specified thickness and protrudably formed along the width direction is installed, and
the second reinforcement piece with a specified thickness along the length direction crossing at right angles with the width direction of the lever and protrudably formed continuously from the first reinforcement piece is installed.
According to the above configuration, the Roberval""s mechanism 2 and the lever 4 are separated, and to this lever 4, bridges 29a, 29b for linkage and fixing are installed between the fixed section 30 and the mobile section 32.
These bridges 29a, 29b are cut off after the lever 4 is assembled to the Roberval""s mechanism 2.
By this, it is possible to install the lever 4 with the size of each section maintained at the time of assembly, enabling easy assembly and improving the assembly accuracy.
In addition, because of the configuration in which the lever comprises the fixed section 30 and the mobile section 32, and fulcrums A and B are formed at the spring section 34, high-accuracy measurement that provides the attenuation rate of the specified force is achieved.
In addition, to the free end 4b of the lever 4, balance driving means 6, position detection sensor 42, and lever travel restricting means are installed.
And by mounting one balance driving means 6 to the one step higher fixed surface 4ba and the other to the stepped surface 4bb, even if the fixing member 45 for fixing these is thermally expanded and the stepped surface 4bb is subject to the influence, it is possible to prevent the plane position of the fixed surface 4ba from varying in the displacement direction of the lever 4.
By this, the driving characteristics can be kept constant without generating variations in mounting height position of balance driving means 6, free of tilts, and without generating variations in control current.
To this lever 4, the first and the second reinforcement pieces 38, 39 which cross at right angles each other and are protrudably formed are installed, enabling the lever 4 to provide the specified rigidity even if it is not a block lump and at the same time the size and the weight can be reduced.
In order to achieve the above objects, according to the present invention,
(9) it is possible to provide the electronic balance recited in Item (1) characterized in that a pair of upper and lower Roberval""s sections are formed by hollowing a solid metal material block and with the specified length via thin-wall spring section between the fixed section and the mobile section, and
the Roberval""s mechanism moves the mobile section applied with the load of the substance to be weighed in the horizontal state.
In order to achieve the above objects, according to the present invention,
(10) it is possible to provide the electronic balance recited in Item (9) further comprising a restriction section that is equipped between the fixed section and the mobile section of the Roberval""s mechanism and that forms a clearance for restricting the mobile range of the mobile section.
In order to achieve the above objects, according to the present invention,
(11) it is possible to provide the electronic balance recited in Item (10) characterized in that the restriction section is formed by hollowing the solid metal material block together with the Roberval""s mechanism, and the restricting clearance section cut in the form of streak for restricting the mobile range of the mobile section is installed at the beam section that links the fixed section to the mobile section of a pair of upper and lower Roberval""s sections.
In order to achieve the above objects, according to the present invention,
(12) it is possible to provide the electronic balance recited in Item (11) characterized in that the fixed section and the mobile section of the lever are linked and fixed to the fixed side and the mobile side, respectively, via the restricting clearance section.
According to the above configuration, the Roberval""s mechanism 2 and the lever 4 are formed separately, and to the lever 4, bridges 29a, 29b for linkage and fixing are installed between the fixed section 30 and the mobile section 32.
The bridges 29a, 29b are cut after they are assembled to the Roberval""s mechanism 2.
By this, it is possible to mount the lever 4 with the size of each section maintained at the time of assembly, achieving easy assembly and improving the assembly accuracy.
In addition, because the lever 4 comprises the fixed section 30 and the mobile section 32, and fulcrums A and B are provided at the spring section 34, the high-accuracy measurement with the attenuation rate of the specified force will be enabled.
To the free end 4b of the lever 4, balance driving means 6, position detection sensor 42, and lever travel restriction means are installed.
And by mounting one balance driving means 6 to the one step higher fixed surface 4ba and the other to the stepped surface 4bb, even if the fixing member 45 for fixing these is thermally expanded and the stepped surface 4bb is subject to the influence, it is possible to prevent the plane position of the fixed surface 4ba from varying in the displacement direction of the lever 4.
By this, the driving characteristics can be kept constant without generating variations in mounting height position of balance driving means 6, free of tilts, and without generating variations in control current.
To this lever 4, the first and the second reinforcement pieces 38, 39 which cross at right angles each other and are protrudably formed are installed, enabling the lever 4 to provide the specified rigidity even if it is not a block lump and at the same time the size and the weight can be reduced.
In order to achieve the above objectives, according to the present invention,
(13) it is possible to provide a manufacturing method of an electronic balance comprising:
a step for preparing a Roberval""s mechanism containing a fixed section, a mobile section that is applied with the load of the substance to be weighed and moves in the vertical direction with respect to the fixed section, and a pair of upper and lower Roberval""s sections that link the fixed section and the mobile section,
a step for preparing a lever that is configured separately from the Roberval""s mechanism, has one end, the other end, and fulcrums, is located between a pair of the upper and the lower Roberval""s sections of the Roberval""s mechanism, receives the motion of the mobile section of the Roberval""s mechanism with the one end, and allows the other end to displace via the fulcrums,
characterized in that the step for preparing the Roberval""s mechanism has a step for forming a lever housing section that enables the lever to be inserted into the Roberval""s mechanism in the longitudinal direction and enabling the lever to be located between a pair of the upper and the lower Roberval""s sections, and
the step for preparing the lever has a step for containing the fulcrums for obtaining the attenuation amount of the specified force from the one end section to the free end of the lever and forming the fixed section and the mobile section in the lever,
a step for forming bridges for fixing and keeping the positions of the fixed section and the mobile section between the fixed section and the mobile section of the lever, and
a step for cutting the bridges after fixing the lever to the Roberval""s mechanism.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.